Lengthen the Growing Season Without a Greenhouse

How to lengthen the growing season without a greenhouse using plastic tunnels, includes information on how to build the tunnel cloche, the cold frame, how to use a cloche or frame and venting the cloche and cold frame.

By Susan Glaese, Bob Kornegay, and the MOTHER EARTH NEWS staff

| September/October 1985

Bob harvests fresh greens from the tunnel cloche.

PHOTO: MOTHER EARTH NEWS STAFF

Learn how to lengthen the growing season to grow winter greens without the use of a greenhouse. (See the extended garden photos and diagrams in the image gallery.)

All right, so don't have a $5,000 solar greenhouse. That doesn't mean you can't grow your very own fresh winter greens.

Fall. A few lights frosts, some frantic scrambling to pick
everything salvageable from the garden, and then—
wham ! A hard freeze hits. All your plants die.
Time to call it quits . . . another gardening year is
finished.

Ahhh, but wouldn't it be nice if you could keep
your crops growing? If you could lengthen the growing season, step outdoors in the
winter and harvest a few vegetables to sustain you through
those long months of preserved and purchased produce?

Well, the good news is that you can do just that.
The better news is that doing so won't cost you an arm and
a leg; we're not talking here about building a full-sized
solar greenhouse. And the best news is that—if you
hop to it—you can do it this very fall, in time to
have your own cold-weather harvest.

This article will tell you how to build MOTHER's gardeners'
two favorite low-cost, season-extending devices . . . how
to use and maintain them . . . and what crops to raise in
them.

The Garden Tunnel Cloche

Collect some 2 foot pieces of rebar, 5 feet to 10 feet lengths of 1/2 inch
PVC pipe, one sheet of 6- to 8-mil clear plastic, and two
pieces of rope, and you've got all the ingredients for a
tunnel cloche. It's easy to build, portable—you can
even construct it right over a bed of already established
fall greens—and quite inexpensive (it'll cover 48
square feet for around $15).

And this simple crop saver really works! Last fall Bob
Kornegay tunnel-cloched a 20-square-foot bed of spinach
behind the low-cost permaculture homestead at MOTHER's
Eco-Village. The greens—which had been sown outdoors
in September—made it fine through the winter in our
4,200-degree-day climate . . . including the record-breaking
night when the mercury hit 16 degrees Fahrenheit below zero! During
those cold months, they grew sparsely: just enough so Bob
could harvest fresh leaves for salads about every other
day. By the end of February, though, he was giving salad
leaves away. And come March, he had all that he could cook
up, eat raw, and freeze!

Figure 1 in the image gallery shows the parts of a PVC tunnel cloche. To put one
together, all you have to do is drive two-foot lengths of
rebar (iron reinforcing rod) into the ground every three or
four feet on either side of the growing bed. Bend a PVC
hoop over each set of rebar pieces. (The exact length of
the PVC will depend on the width of your bed: five feet of
pipe for a two-foot-wide bed, eight feet for a three-foot
bed, nine for four, and ten for five.) Drape your plastic
on top and then secure it at the base to keep that cold
night air out. You can do this by simply weighting down the
sides and ends with rocks, or by bunching the ends together
with ropes and snugly securing those lines. Bob has found
that the only time he really needs to tie his cloches' ends
is during March, when our area receives strong spring
winds. Then he uses an adjustable slipknot—shown in
Figure 2 in the image gallery—to keep those cords tight.

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There are other simple ways to make tunnel cloches. You can
make your hoops of spring steel poked into the ground. Lay
your plastic over those, then run a second hoop or string
right next to each of the supporting ones to hold the
plastic in place (see Figure 3 in the image gallery). Or you can use reinforcing
wire mesh arched over the bed (cut the material so both
sides have lots of wire ends to poke into the ground) and
cover that with plastic (Figure 4 in the image gallery).

The Garden Cold Frame

Tunnel cloches are definitely the "hot" plant protector at
the Eco-Village these days—we're using them more and
more. But we're far from abandoning our other small-scale
season extender: the cold frame.

A cold frame, essentially, is a bottomless box (usually of
wood) that faces south, is higher in the back (the north
side), and is covered with glass or plastic. Cold frames
are durable, attractive, easy to use, and—because of
their increased insulation—probably better at
protecting plants from extreme cold than the all-plastic
cloches. On the other hand, they do cost more to construct
than tunnel cloches: The materials for the 4 foot by 6 foot model
shown in Figure 5 in the image gallery cost around $150, not counting the
glazing. And although you build such a miniature greenhouse
from the bottom up, you should design it from the top down
. . . in other words, it's easier to get your glass (or
other glazing) first and build the frame to fit it. If you
can scrounge up some usable windows or glass door panels,
you'll have trimmed a considerable expense.

You'll want to build your cold frame so the top slants
southward, but don't worry about trying to get the "best"
sun-catching angle; that's usually not critical. Do be sure
to paint the interior white to help diffuse the admitted
light, though.

Unless you'd prefer to have a portable cold frame, you'll
want to lay some type of foundation. You can use concrete
block, rot-resistant wood (such as locust, cedar, or
cypress), or lumber painted with a latex acrylic paint or a
homemade preservative of copper naphthenate or linseed oil.
(Never use creosote or pentachlorophenol on a cold frame.)
Lay this below frost level and insulate it with closed-cell
foam board insulation. You might also be wise to place
gravel under and around your frame's foundation to improve
its drainage and to help protect the wood.

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For glazing, use glass if you scrounged up windows . . .
6-mil polyethylene if you want to skimp (and have a very
temporary covering) . . . or a fancy fiberglass-reinforced
plastic (FRP) if you want something durable (and pricey).
Since your biggest heat loss will be through the top of the
cold frame, you'd do well to double-glaze the top. One of
the most practical and cost-effective ways to do that is to
use glass on the top and plastic underneath. The glass will
help filter ultraviolet rays, which deteriorate plastic.
And if the glass should ever break, the plastic may help
catch the pieces!

You'll need to devise some way to open the windows. You can
either hinge them in the back or—as we
did—build channels for the units so you can slide
them up and down (which gives finer ventilation control).
In addition, you may want to lay down pliable weather
stripping where the glazing meets the sides of your frame
to help seal that junction.

Up to a certain point, plants double their growth
rate for every 10 degrees Fahrenheit rise in soil temperature, so
anything you do to help keep the ground warm is going to
pay off. For starters, insulate the sides of the frame with
some closed-cell foam board . . . or simply pile hay or
even soil around it.

You can further improve the frame's thermal performance by
adding some heat-retaining mass to it. If you insulated the
foundation, you're effectively using the interior soil
itself as thermal mass. You can also stack 30-gallon
water-filled drums, painted black, along the back wall,
either on the ground or partly buried in the soil.

And if you really want to help heat the frame bed, bury a
mixture of fresh manure and straw or wood shavings under
the bed's soil . . . and create what's called a hotbed. The
decomposing pile will generate heat for your plant's soil.
Don't use manure alone for this purpose: It'll cook too hot
and too quickly, possibly harming your plants with excess
ammonia gas.

How to Use a Cloche or Frame in the Garden

If you're new to this art of gently coaxing plants to grow
out-of-season, you need to know that such "solar-intensive"
gardening is demanding. So start small—just try out
one tunnel cloche or cold frame this season—and
construct your plant shelter as near to your house as
possible.

Since you will be working with a limited amount of
sheltered space, do everything you can to utilize it
efficiently. Plant in wide beds, not in single rows, and
eat all you harvest (including broccoli leaves, carrot
tops—in salads—and cut-up greens stems). Just
as important, create the best possible soil for your crops.
Compost and fertilizing amendments are vital, since most of
the commonly grown winter vegetables are heavy feeders and
will be growing under somewhat stressful conditions.

Maintaining proper moisture levels is another way of
promoting maximum growth and reducing plant stress. You'll
probably need to water deeply only once a week in the fall
and spring . . . and even less during the coldest months of
winter. You certainly don't want to overwater, since that
can lead to damping-off and other diseases.

Just as critical as the amount of liquid you provide is
when you supply it and what temperature
it is. Never water a cold frame or cloche in the evening;
that would only make the plants colder during the coming
night. If you have no means of heating your liquid, the
best time to water is in the morning—then the heat of
the day can help warm the water, air, and soil together.
(The water will also provide some additional thermal mass
to store that day's heat.) Far better is heating the liquid
before you give it to the plants. Hot tap water will do
fine. Or simply leave plastic gallon jugs, painted black,
in your plant shelter. On a good sunny day, those jugs may
reach 80 to 85 degrees Fahrenheit by late morning. The water will then
be ready to use . . . probably just at the time your frame
needs to be opened up for venting, anyway!

The Big Hitch: Venting

That beings us to the worst inconvenience of such
solar-intensive gardening: venting. We know, we
know—you went to all this work to create a plant
environment that captures and retains as much heat as
possible. Ironically, though, you've got to let some of
that warmth out on many sunny days. Otherwise, your plants
may get too hot, the gases they outbreathe may reach
harmful levels, and the interior humidity may get high
enough to create blissful conditions for molds, mildews,
and fungi.

So whenever the temperature inside your frame or cloche
begins to soar, you've got to crack it open a bit (don't
just fling it open, as the sudden cold may shock your
plants). Some days you may find yourself making several
trips to ventilate and close systems—a prime reason
for locating the winter garden as close to your house as
possible.

As Susan puts it, managing winter frames and cloches
requires "being married to the garden." Just keep reminding
yourself of the extra-fresh food you get to eat at a time
of year when store-bought produce is low-quality, shipped
long distances, and heavily sprayed.

Growing Good Crops

Plants that have long maturity dates or require pollination
to set fruit are poor choices for frame and cloche
gardening. Cabbages, broccoli, and cauliflower handle cold
weather better but take up a lot of space for what they
yield. Root crops such as carrots and parsnips can be good
choices. In most climates, however, you can plant these in
summer—we start our winter carrots in
mid-July—cover then, in late fall with several inches
of straw, and pull back that covering whenever you want to
harvest some. (They'll be easier to find under that mulch
if you plant them in little "channels" spaced 5 inches or 6 inches
apart across the bed.) "Storing" root crops under mulch
leaves your frames and cloches free for other crops.

So what are the best choices for sheltered
growing? The most obvious selections are the "pick and come
again" leaf crops such as mustard, Swiss chard, ruby chard,
parsley, kale, collards, spinach, and hardy leaf lettuces.
But greens aren't the only good choices: New research has
shown that many oriental vegetables are
wonderfully adapted to frame and cloche growing conditions.
Bok (or pak) choi, daikon radish, michili, gai lohn,
shingiku, and wong bok cabbage are just a few of these
plants. If you're not already familiar with using these in
stir-fried dishes, salads, soups, casseroles, quiches, and
more, now may be just the time to experiment. (See the
sidebar for some suggested cold-season varieties and
sources.)

Extending the Growing Season: Grow to It!

Both cloches and cold frames are useful for all seasons of
the gardening year. Hardy vegetables planted in the
shelters in mid fall may yield abundant, super-early spring
produce. Later in the spring, the plant houses can be used
to harden of vegetable seedlings and start cuttings of
herbs or ornamentals. If you replace the panes or plastic
with a gardener's shade cloth, you've got a place to raise
summer lettuce. And you can set a cloche or portable cold
frame in the garden itself to overwinter half-hardy
perennials . . . to dry and warm a section of the garden
you want to plant in early spring . . . or to shield some
tender transplants you want to gently heel in. (In this
last case, try draping a white bed sheet over the frame or
cloche for a day or two to moderate both light and heat.)

So why wait? Start this fall with one tunnel cloche or cold
frame, and try your own season-extending garden experiments.
If all goes well, while your friends are picking their way
through seed catalogs and dreaming of spring, you'll be
picking your way through the crops of your own wintertime
harvest!

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